Nothrotheriops shastensis (Sinclair, 1905)

Davis, Matt, Nye, Benjamin D., Sinatra, Gale M., Swartout, William, Sjӧberg, Molly, Porter, Molly, Nelson, David, Kennedy, Alana A. U., Herrick, Imogen, Weeks, Danaan DeNeve & Lindsey, Emily, 2022, Designing scientifically-grounded paleoart for augmented reality at La Brea Tar Pits, Palaeontologia Electronica (a 9) 25 (1), pp. 1-37 : 23-24

Nothrotheriops shastensis

( Figure 15 )

Appearance. Reconstructions of extinct ground sloths are likely more tenuous than those of extinct carnivorans and ungulates because ground sloths lack close living relatives ( Davis et al., 2018) or even functional analogues among modern fauna (Lopes et al., 2016; Davis, 2017). However, due to well preserved remains of the Shasta ground sloth ( Nothrotheriops shastensis ) (Lull, 1929), we likely know more about its appearance than any other extinct sloth (Kurtén and Anderson, 1980). Our model ( Figure 15 ) follows an archetypal plasticine sculptural reconstruction by Lull (1929) based on a desiccated Shasta ground sloth (YPM 13198) found preserved in guano inside a fumarole in Aden Crater, New Mexico. There is little doubt his reconstruction accurately captures the general posture of the living sloth as the bones of YPM 13198 were held in articulation by preserved ligaments and tendons (Lull, 1929). Additionally, five patches of skin including one with 45 mm long pale-yellow hair were also found on the specimen.

DAVIS ET AL.: LA BREA TAR PITS PALEOART

For cranial anatomy, we relied on the detailed muscular reconstructions of Naples (1987) although we gave the Shasta ground sloth face coloration common to three-toed sloths (Bradypus spp.) for purely artistic reasons.

One shortcoming of both the Shasta and Harlan’s ground sloth ( Paramylodon harlani , discussed below) models ( Figures 15 , 16 ) is the blockiness of the appendages. Given the constraints of our low poly style and how the models needed to be rigged and animated, these models necessarily exhibit a somewhat clumsy rendition of the proportions of the various digits and claws. Although much research has gone into the skeletal structure of ground sloth appendages ( McDonald, H.G., 2012), it is not entirely clear what the external appearance of most ground sloth pedes and manus would have looked like. Digits on the same pes or manus can range from vestigial nubs to long claws with keratinous sheathes. Detailed comparative analyses and reexamination of specimens like YPM 13198 could lead to more accurate external reconstructions of these important features. We acknowledge helpful expert guidance from H. Gregory McDonald on the appendages of both ground sloth species discussed here.

Behavior. The general movements of our animations follow those of the Shasta ground sloth done for Ice Age Giants (2013), a large budget BBC documentary featuring La Brea Tar Pits.

Harlan’s Ground Sloth

Figures

FIGURE 15. Low poly reconstruction of the extinct Shasta ground sloth (Nothrotheriops shastensis). To view this model in 3D, please see the online version of this article.

FIGURE 16. Low poly reconstruction of the extinct Harlan’s ground sloth (Paramylodon harlani). To view this model in 3D, please see the online version of this article.